What is the theory that would explain the indus river valley migration?

Indo-Aryan Migration theory:

Explanation:

A theory suggesting the Harappan culture of the Indus River Valley was assimilated during a migration of the Aryan people into northwest India. monsoon: Seasonal changes in atmospheric circulation and precipitation; usually winds that bring heavy rain once a year.

the  seven  days  battles  were  a series of seven battles over seven  days from june 25 to july 1, 1862, near richmond, virginia,  during  the american civil war. the  seven  days ended with mcclellan's army in relative safety next to the james river, having suffered almost 16,000 casualtiesduring  the retreat.